An audio-tactile traffic signalling system provides combined audible and tactile signals to supplement the normal pedestrian light signals at controlled pedestrian crossings. Two types of audio-tactile signals are provided:
(a) a locating signal which enables the visually handicapped person to locate the push-button assembly and register a demand. This signal is continuously emitted except when the associated pedestrian light signal is green, PA1 (i) a fundamental frequency of between 400 Hz and 600 Hz; PA1 (ii) a spectral bandwidth extending to at least 5 kHz; PA1 (iii) a sinusoidal waveform with an amplitude decaying exponentially with a time constant of 50 ms; and PA1 (iv) a pulse repetition frequency within the range 8 Hz to 10 Hz. PA1 (a) a nominal 240 volt AC mains supply, and, PA1 (b) the nominal 240 volt AC active feed to the associated pedestrian green signal lamps,
(b) a crossing signal which is emitted only when the associated pedestrian light signal is green.
The tranducer for the audio-tactile signal is located within the push-button assembly and acts on the front surface of the push-button housing. The associated electronic equipment to drive the tranducer is contained in a separate housing remote from the push-button assembly, for example, adjacent to the traffic lights. The remote driver unit or housing is hard-wired to the transducer in the push-button assembly.
The audible locating signal as defined by the Department of Main Road of New South Wales, Australia specification ATS/2 has the following operational characteristics:
(a) a fundamental frequency within the range 900 Hz to 1100 Hz; PA0 (b) a spectral bandwidth extending to at least 5 kHz; PA0 (c) a rectangular waveform with a rectangular modulation envelope of between 20 ms and 30 ms duration; PA0 (d) a pulse repetition frequency within the range of 0.5 to 0.6 Hz; PA0 (e) an output sound pressure level which is automatically adjusted to maintain a constant relationship with the instantaneous A-weighted ambient noise level over the range 35 to 75 dB (A); and PA0 (f) fixed upper and lower output sound pressure levels which are maintained when the ambient noise is outside the range specified in (e) above. PA0 (a) an initial transition stage comprising a single pulse of a constant amplitude square wave having a frequency changing exponentially from 2 kHz to 500 Hz with a time constant of 50 ms; and PA0 (b) a second stage having the following operational characteristics: PA0 (a) the area over which the tactile signal is generated shall be at least 30 mm diameter located immediately above the push-button switch, using a pedestrian push-button switch assembly complying with specification No. PB/5. PA0 (b) the tactile signal shall have a sinusoidal waveform with a frequency lying between 100 Hz and 175 Hz. PA0 (c) the tactile signal shall be in-phase with the audible signals specified under Clauses 3.2 and 3.3. The signal shall comprise an integral number of cycles (between 3 and 8) commencing and finishing on a zero crossing, with a duration of not less than 30 milliseconds and periodicity corresponding to the audible signal. PA0 (d) the tactile signal output shall have a peak acceleration exceeding 1 g (9.81 m/s.sup.2). This will necessitate an output voltage in the range 8 to 11 V peak-to-peak, depending upon frequency, for the nominal sensitivity of the transducer specified in FIG. 2.
In order to comply with requirement (e), a microphone is mounted within the remote driver unit or housing to monitor the ambient noise level and to provide a suitable control signal.
The audible crossing signal as defined by the above specification ATS/2 has two separate stages:
The tactile signal generated on the front of the push button assembly housing is defined by specification ATS/2 as follows:
The remote driver unit or housing contains two isolating transformers connected to:
for operation of the audio-tactile tranducer as well as the associated electronic circuits.
Although the applicant's prior art audio-tactile traffic signalling system of the kind described above has achieved wide commercial acceptance, there is a need for an improved system which is simpler in constructional detail and cheaper to produce.